*{
    margin: 0;
    padding: 0;
    list-style: none;
}
body{
    background: lightblue;
}
.container{
    width: 1200px;
    margin: 0 auto;
}
.col{
    float: left;
    width:33.333333%;

    /*加装饰效果*/
    height:100px;
    background: lightpink;
}
@media (max-width:600px) {
    .container{
        width:100%;
    }
    .col{
        width:100%;
    }
    body{
        background: lightgreen;
    }
}
.container::after{
    content: "";
    display: table;
    clear: both;
}
